Could it be that cabin crew are human beings and occasionally miss things ? Granted in a crash, it becomes important... but if you were checking 100 different seats were upright day in, day out, could you achieve 100 % accuracy every day ? If something had happened domestically (eg kid is ill, had an argument with spouse, nasty threatening letter chasing a debt) checking seats are upright probably wouldn't get the same level of scrutiny as normal. You're an adult... you heard the verbal announcement.